A mission called Dawn is unlike any that's ever been attempted. If all goes well, it will orbit not one body, but two. It's scheduled to arrive at its first port of call on Saturday: Vesta, one of the largest asteroids.

RUSSELL: This is really innovative because it explores the bodies in the way that you might do in the movies, in science fiction stories.

Christopher Russell is Dawn's lead scientist.

RUSSELL: And that is, you take your spacecraft and you go and do one set of explorations, and when you decide to leave you can leave, and you can go over to another body and explore it.

And a year from now, that's just what Dawn will do -- it'll head for Ceres, the largest asteroid of them all.

Asteroids are relics from the dawn of the solar system -- hence the mission's name. They should preserve a record of conditions at the time Earth and the other planets were born. In fact, the planets formed as objects like the asteroids -- as well as the icy comets -- stuck together to form bigger and bigger bodies.

Dawn will use a suite of instruments to map Vesta's surface. It'll also map the chemical elements on the surface, as well as the minerals that make up Vesta's rocks. It'll also measure the asteroid's gravity field, which will help probe its interior, which probably contains a dense metallic core.

Once that work is done, it's off to Ceres -- with the help of small but hardworking rocket engines and the power of the Sun. More about that tomorrow.